The oligomerization of light olefins, such as propene and butene, represents a major industrial production and sustainable route for the production of liquid synthetic fuels, free of sulfur and aromatics. These processes allow the production of mixtures of olefinic compounds in the range of gasoline or diesel, depending on the selectivity of the catalyst and the operating conditions.
As described in the state of the art, at high temperatures (>300° C.) and low pressures (≦30 bar) the gasoline yield is increased while high pressures and low temperatures favor formation of heavier oligomers in the diesel fraction.
Alkene oligomerization of low molecular weight to products in the diesel range is achieved with the use of acid catalysts, in such a way that the reaction mechanism involves formation of carbenium ions. To obtain high quality diesel product the degree of branching should be restricted and this problem is solved via two possible strategies: by modifying the acid centers (either their strength or the strength of their environment) or by applying the concept of “shape selectivity”, using the catalyst with channels of the adequate size to allow the control of the oligomers growth and the branching degree thereof (Catal. Today 77 (2003), 467).
In the literature there are many solid acid catalysts for the oligomerization of light olefines to medium distillates reported.
The solid phosphoric acid (SPA) has been described as catalyst for the oligomerization of olefins derived from Fischer-Tropsch, for the production of “polymerization gasoline” and medium distillates in Ind. Eng. Chem. 28 (1936) 1461, Energy Fuels 20 (2006) 439 and 1799, and Appl. Catal. 308 (2006) 204. It has also been described, as a catalyst in oligomerization processes of streams free from olefines, the mesoporous material Si/Al MCM-41 (Catal. Today 75 (2002) 125). These materials have been tested with and without small amounts of metal (Ni, Rh or Pt).
Other catalysts studied for oligomerization reactions of olefines to diesel are clays, as described in Catal. Commun. 6 (8) (2005) 25 568 and Clay Minerals (3) (1990) 355, heteropolyacids and metal salts thereof (Preprints ACS Div. Petrol. Chem. 36 (4) 1991) 605) and cation exchange resins described in Appl. Catal. 16 (2) (1985) 193.
Medium pore zeolites have proved to be the most suitable ones for high-quality medium distillates in olefin oligomerization processes. Most studies reported in the literature (eg in AIChE J. 32 (9) (1986) 1526) are based on the MFI zeolite. Furthermore, in various patents different structures with 10-membered rings are claimed for this process.
U.S. Pat. No. 4,227,992 and U.S. Pat. No. 4,211,640 claim ZSM-11 as catalyst for olefin oligomerization processes and mention other zeolites such as ZSM-12, ZSM-21 and mordenite TEA. GB2106131 and GB2106533 claim the use of ZSM-5 and ZSM-11, in their protonic form, for the oligomerization of light olefins with a selectivity of 25% by weight, to diesel product with a cetane number of 75.
In the 90s, several medium pore zeolites and their use, as catalysts for the oligomerization of light olefins to high quality oligomers and essentially linear ones, which could become lubricating oils of high viscosity index (VI), were patented, diesel with high cetane number and/or chemical intermediates with high added value. Most of these zeolites were treated to increase their selectivity eliminating the surface acidity in such a way that the quality of the product is increased, what is also known as selectivation process. In U.S. Pat. No. 5,234,875 a ZSM-23 zeolite selectivated by coking is described, the performance thereof to slightly branched products is considerably increased when compared with the unmodified catalyst. slightly branched products increases significantly compared to the unmodified catalyst described. In U.S. Pat. No. 5,284,989 three medium pore zeolites, ZSM-22, ZSM-23 and ZSM-35, are described, treated with dicarboxylic acid to deactivate their surface acidity, for the production of hydrocarbons with a low branching degree, in propylene oligomerization processes. These products can be used as alkylating agents for preparing and biodegradable alkylbenzenes and alkylphenylsulfonates.
Several patents (WO95/19945; WO95/22516; U.S. Pat. No. 6,143,942) claim the use of different medium pore zeolites such as ZSM-22, ZSM-57, ZSM-5, alone or in combination, in light olefin oligomerization processes. Thus, they are able to control the degree of oligomerization of olefins, for example to propylene trimer.
In WO93/082780 zeolite ZSM-23 is selectivated with different contents of collidine and is tested in a tubular fixed bed reactor in oligomerization process of butene streams. The reduction in the branching degree as a result of the selectivation is clearly shown and, in addition, it is observed that the reduction in the branching degree and the increase in selectivity to mono-branched isomers are achieved by deactivating the between 25 and 30% of the acid centers.
US2006/0194999 discloses a catalyst for oligomerization processes that comprises a MWW type acidic zeolite as a substitute for solid phosphoric acid, that produces products corresponding to the gasoline fraction products, with high octane number, and other motor fuels such as diesel.
Silicalite containing Al and Ti has also been proposed as a catalyst for oligomerization of light olefins to high quality jet fuel (jet fuel) diesel fractions (31 Gas Oil (2005) 70; EP0293950; EP1249486).
FR2887538A1 describes the use of different zeolites, MEL, ITH, MFI, NES, EUO, ERI, FER, CHA, MFS, MWW, MTT, TON and MOR, which have been previously dealuminated in a first step, followed by a further addition of silicon, and that have been finally transformed to their protonic or acid form.
FR2894850A1 describes the use of MEL, ITH, MFI, NES, EUO, ERI, FER, CHA, MFS, MWW, MTT, TON and MOR zeolites in oligomerization processes for the obtaining of diesel and jet fuel. The zeolites are impregnated with metals of the series VIB and VIII followed by gas phase deposition of amorphous SiO2 with pore size greater than the pore of the zeolites. The catalyst is used in its acid or protonic form.
FR2837199 and FR2837213 disclose the use of zeolites, MEL, MFI, NES, EUO, FER, CHA, MFS, MWW, NU-85, NU-86, NU-88 and IM-5 as catalysts for the oligomerization step in multistage processes of hydrocarbon conversion.
WO2002/36491 discloses the use of UZM-4 zeolite as catalyst in oligomerization processes, but the patent does not include examples of catalytic applications.
WO2007/079038 describes the use of SSZ-74 zeolite catalyst in oligomerization processes, but the document does not include examples of catalytic applications.
The present invention relates to a process of oligomerization of alkenes based on the use of a catalyst containing ITQ-39, described in WO2008/092984, in which the catalyst is not only very active but it increases the selectivity to diesel fraction and is highly stable against deactivation with the reaction time (TOS: Time on Stream) compared with other catalysts reported to date